Induction of rat hepatic cytochromes P-450 by environmental nitropolycyclic aromatic hydrocarbons.

Nitrated polycyclic aromatic hydrocarbons (PAHs) are environmental contaminants that result from various incomplete combustion processes. We have examined the activity of hepatic microsomal enzymes in rats pretreated with a series of environmentally occurring nitrated PAHs including: 1- and 4-nitropyrene, 1,3-, 1,6- and 1,8-dinitropyrene, 6-nitrochrysene, 7-nitrobenz[a]anthracene, 3-nitrofluoranthene, and 1-, 3-, and 6-nitrobenzo[a]pyrene. None of the compounds increased the cytochrome P-450 content more than 2-fold. 1,8-Dinitropyrene, 6-nitrochrysene, and 1- and 3-nitrobenzo[a]pyrene significantly increased arylhydrocarbon hydroxylase activity 2- to 8-fold higher than solvent-treated controls. The induction of 7-ethoxycoumarin O-deethylase activity paralleled that found with arylhydrocarbon hydroxylase. The maximum induction of aminopyrine N-demethylase was only 1.5-fold, and none of the nitrated PAHs caused significant increases in epoxide hydrase or NADPH-cytochrome c reductase. 1-Nitropyrene reductase activity was induced by each of the compounds with the exception of 6-nitrobenzo[a]pyrene. The greatest increase was caused by 1-nitrobenzo[a]pyrene followed by 1,3-dinitropyrene, 3-nitrobenzo[a]pyrene and 6-nitrochrysene. These data suggest that nitrated PAHs may potentiate the effects of subsequent exposures to various chemical carcinogens.